1. Technical Field
Apparatuses and processes for the recovery of 1-butene from a mixed C4 feed stream are disclosed. More specifically, this disclosure is directed toward methods and apparatuses for the separation of 1-butene from a mixed C4 feed of 1-butene, 2-butene, isobutane and n-butane, using a single distillation column.
2. Description of the Related Art
Olefinic hydrocarbons are feedstocks for a variety of commercially important reactions that yield fuels, polymers, oxygenates and other chemical products. In the industrially important OXO process, olefins react catalytically with carbon monoxide and hydrogen to give aldehydes. Olefins are polymerized by heating with catalysts to give high-octane gasolines, plastics, and synthetic rubber.
The specific isomer, the position of the double bond and the degree of branching of an olefin all may be important to the efficiency of a chemical reaction or to the properties of the final product. Thus, it is often desirable to isomerize olefins to increase the output of the desired isomer. Further, because the distribution of isomers in a mixture of olefins is rarely optimum for a specific application, the separation of isomers is an important industrial process.
One group of olefins, butenes (also known as butylenes, C4H8), serve as intermediates in the preparation of a variety of organic compounds. Butenes are formed during the catalytic cracking of petroleum to produce gasoline. Butenes can also be prepared commercially by the catalytic dehydrogenation of butanes. Butenes include four isomeric compounds belonging to the series of olefinic hydrocarbons: 1-butene; cis-2-butene; trans-2-butene; and isobutene. All four butene isomers are gases at room temperature and pressure.
Butenes are among the most useful olefins having more than one isomer. Butenes are utilized for the production of octanes, which are traditional components of gasoline. Butenes are converted to octanes by reacting butenes with isobutane or by dimerizing two butenes to form octenes, which, upon hydrogenation, yield octanes. On treatment with water in the presence of catalysts, butenes are transformed into secondary and tertiary butyl alcohols, which are used as commercial solvents.
Secondary-butyl alcohol and methylethyl ketone, as well as butadiene, are important derivatives of 2-butenes. The most important derivative influencing isobutene and 2-butene isomer demand may be methyl t-butyl ether (MTBE) which is an important component of gasoline. Isobutene also finds application in such products as methyl methacrylate, polyisobutene and butyl rubber.
Demand for 1-butene has been growing rapidly based on its use as a co-monomer for linear low-density polyethylene and as a monomer in polybutene production 1-butene is also used in the manufacture of other polyethylenes, polypropylenes, polybutenes, butylene oxides and the C4 solvents secondary butyl alcohol (SBA) and methyl ethyl ketone (MEK). The co-polymerisation of ethylene and 1-butene produces a form of polyethylene that is more flexible and more resilient. 1-butene can also help to create a more versatile range of polypropylene resins.
The isolation of 1-butene from mixed feed of butane and the other butane isomers currently requires at least two distillation processes as best seen in FIG. 1. In the described process, the first distillation performed in the column 10, a mixed C4 feed enters the column 10 through the line 11. 1-butene and isobutane are separated from butane and the 2-butenes of the mixed C4 feed. Specifically, 1-butene and isobutane leave the column from the overhead line 12, pass through the condenser 13/collector 13′ and are fed to the next column 14 through the line 15. Part of the at least partially condensed isobutane/1-butene stream is recycled back to the column 10 through the line 16 and control valve 17. A mixture of n-butane and 2-butene exits the column 10 through the bottoms outlet line 18 which is connected to a product line 19 and a recycle line 21. Part of the butane/2-butene stream passes through the recycle line 21 and heat exchanger 22 where it is reboiled prior to reentering the column 10 as shown.
In the second distillation, carried out in column 14, the isobutane and 1-butene are separated. Specifically, the isobutene/1-butene feed enters the column 14 through the line 15 and isobutane exits the column 14 through the overhead outlet line 23, passes through the condenser 24/collector 24′ before proceeding on to the outlet line 25. Part of the isobutane overhead product is recycled through the line 26 and control valve 27. The 1-butene leaves the column 14 through the bottoms outlet 28 and product outlet line 29 as controlled by the control valve 31. Part of the bottoms outlet 28 is recycled through the heat exchanger or boiler 32 before re-entering the column 14.
Because of the increasing demand for 1-butene, there is a need for a more efficient process for separating 1-butene from the other butene isomers, isobutane and n-butane